Package-on-package (PoP) structure including stud bulbs and method

ABSTRACT

Embodiments concern Package-On-Package (PoP) structures including stud bulbs and methods of forming PoP structures. According to an embodiment, a structure includes a first substrate, stud bulbs, a die, a second substrate, and electrical connectors. The stud bulbs are coupled to a first surface of the first substrate. The die is attached to the first surface of the first substrate. The electrical connectors are coupled to the second substrate, and respective ones of the electrical connectors are coupled to respective ones of the stud bulbs.

This application claims the benefit of U.S. Provisional PatentApplication Ser. No. 61/565,280, filed on Nov. 30, 2011, entitled“Package-On-Package (PoP) Structure and Method,” which application ishereby incorporated herein by reference in its entirety.

BACKGROUND

Electronics can be divided into a simple hierarchy consisting of devicessuch as integrated circuit (IC) chips, packages, printed circuit boards(PCB), and a system. The package is the interface between an electronicdevice, such as a computer chip, and a PCB. Devices are made fromsemiconductor materials such as silicon. Integrated circuits areassembled into a package such as a quad flat pack (QFP), pin grid array(PGA), or ball grid array (BGA), using wire bonding (WB), tape automatedbonding (TAB), or flip chip (FC) bumping assembly techniques. Thepackaged device is then attached either directly to a printed wiringboard or to another type of substrate, which is defined as the secondlevel of packaging.

Ball grid array (BGA) packaging technology generally is an advancedsemiconductor packaging technology, which is characterized in that asemiconductor chip is mounted on a front surface of a substrate, and aplurality of conductive elements such as solder balls are arranged in amatrix array, customarily referred to as ball grid array, on a backsurface of the substrate. The ball grid array allows the semiconductorpackage to be bonded and electrically connected to an external PCB orother electronic devices. The BGA package may be employed in a memorysuch as Dynamic Random Access Memory and others.

A basic flip-chip (FC) packaging technology comprises an IC, aninterconnect system, and a substrate. A function chip is connected tothe substrate with a plurality of solder bumps, wherein the solder bumpsforming a metallurgical interconnection between the chip and thesubstrate. The function chip, the solder bump, and the substrate form aflip-chip package. Further, a plurality of balls form a ball grid array(BGA).

Wire bonding can be used to make the electrical connections from chipcomponents such as chip resistors or chip capacitors to substrate. Twofunction chips are stacked on top of a plurality of substrate layers.The chips are connected to the substrate by a plurality of bonding goldwires. Other form of wires such as aluminum wire can be used, too. Thefunction chips, the gold wire, and the substrate form a wire bonding(WB) package.

Package-on-Package (PoP) is an integrated circuit packaging technique toallow vertically combining, for example, discrete logic and memory ballgrid array (BGA) packages. Two or more packages are installed on top ofone another, e.g. stacked, with a standard interface to route signalsbetween them. This allows higher density, for example in the mobiletelephone/PDA market.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present embodiments, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIGS. 1 through 8 are a first method of forming a package-on-package(PoP) structure according to an embodiment;

FIGS. 9 through 14 are a second method of forming a PoP structureaccording to an embodiment;

FIGS. 15 through 19 are a third method of forming a PoP structureaccording to an embodiment;

FIG. 20 is a single stud bulb according to an embodiment;

FIG. 21 is a single stud bulb with an elongated tail according to anembodiment;

FIG. 22 is stacked single stud bulbs comprising a same materialaccording to an embodiment

FIG. 23 is stacked single stud bulbs comprising different materialsaccording to an embodiment;

FIG. 24 is stacked single stud bulbs, one of which having an elongatedtail, according to an embodiment;

FIG. 25 is a joint with a single stud bulb and a reflowed solderconnector wetted to a pad protection layer according to an embodiment;

FIG. 26 is a joint with a single stud bulb with a greater height and/orelongated tail and a reflowed solder connector wetted to a padprotection layer according to an embodiment;

FIG. 27 is a joint with a single stud bulb and a reflowed solderconnector that is not wetted to a pad protection layer according to anembodiment;

FIG. 28 is a joint with a single stud bulb with a greater height and/orelongated tail and a reflowed solder connector that is not wetted to apad protection layer according to an embodiment;

FIG. 29 is a partial joint according to an embodiment;

FIG. 30 is a joint with a single stud bulb and an inter-metalliccompound (IMC) on a pad protection layer according to an embodiment;

FIG. 31 is a joint with a single stud bulb and an IMC on the single studbulb according to an embodiment;

FIG. 32 is a joint with a single stud bulb and an IMC on a padprotection layer and the single stud bulb according to an embodiment;

FIG. 33 is a partial joint with an IMC on a stud bulb according to anembodiment;

FIG. 34 is a layout view of components of a package structure accordingto an embodiment;

FIG. 35 is a cross section view of components of the package structurein FIG. 34 according to an embodiment;

FIG. 36 is an example PoP structure according to an embodiment;

FIG. 37 is a cross section view of components of a package that includesstud bulbs having a height that extends above a top surface of a dieaccording to an embodiment;

FIG. 38 is a cross section view of components of a package that includesstacked single stud bulbs having a height that extends above a topsurface of a die according to an embodiment;

FIG. 39 is a cross section view of components of a package that includesstud bulbs with elongated tails having a height that extends above a topsurface of a die according to an embodiment; and

FIG. 40 is a cross section view of components of a package that includesstud bulbs having a height that does not extend above a top surface of adie according to an embodiment.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the present embodiments are discussed in detailbelow. It should be appreciated, however, that the present disclosureprovides many applicable inventive concepts that can be embodied in awide variety of specific contexts. The specific embodiments discussedare merely illustrative of specific ways to make and use the disclosedsubject matter, and do not limit the scope of the different embodiments.

Embodiments will be described with respect to a specific context, namelya package-on-package (PoP) structure. Other embodiments may also beapplied, however, to other packages or structures, such as threedimensional integrated circuits (3DIC).

It should be noted that although method embodiments explicitly discussedherein are discussed with respect to a particular order, embodimentscontemplate methods with steps performed in any logical order. Further,throughout the various views and illustrative embodiments, likereference numbers are used to designate like elements.

FIGS. 1 through 8 illustrate a first method of forming a PoP structureaccording to an embodiment. In FIG. 1, a first substrate 10, forexample, a bottom substrate, is provided with pads 12 over a top surfaceof the first substrate 10. An organic solderability preservative (OSP)14 is provided over a top surface of each of the pads 12. The firstsubstrate 10 may be, for example, an organic substrate, a semiconductorwafer, glass, a silicon interposer, an organic interposer, the like, ora combination thereof. The first substrate 10 may comprise, for example,unsingulated or singulated dies and/or interposers. Each die and/orinterposer can comprise active and/or passive devices and/or throughvias. The first substrate 10 may also comprise various layers ofmaterials, such as dielectric layers, passivation layers, and/ormetallization layers.

The pads 12, in an embodiment, are formed directly connected torespective patterns in a top metallization through a passivation layer.In another embodiment, the pads 12 are each a pattern in a topmetallization layer. In further embodiments, the pads 12 can berespective exposed portions of through vias and/or can be formed onrespective portions of through vias. The pads 12, in an embodiment, area metal, a metal alloy, or layers of a metal(s) and/or metal alloy. Inthis embodiment, the pads 12 are copper, and in other embodiments, thepads 12 may comprise copper, gold, aluminum, aluminum copper (Al(Cu)),nickel, the like, or a combination thereof. The pads 12 provide anexterior electrical connection to various devices and/or componentswithin and/or coupled to the first substrate 10.

In FIG. 2, the OSP 14 is removed from each of the pads 12 to expose thetop surfaces of the pads 12. The OSP 14 may be removed by an acceptableremoval process, such as by dispersing a flux on the substrate, achemical solution (acid or alkali), the like, or a combination thereof.

In FIG. 3, a pad protection layer 16 is formed over the top surface ofeach of the pads 12. The pad protection layers 16, in some embodiments,are a metal, a metal alloy, layers of a metal(s) or metal alloy(s), thelike, or a combination thereof. Examples of metals include tin, nickel,palladium, gold, the like, or a combination thereof. The pad protectionlayers 16 may be formed, for example, by immersion plating,electro-plating, electroless-plating, the like, or a combinationthereof. In an embodiment, the pad protection layers 16 are tin formedby immersion plating. In another embodiment, the pad protection layers16 are electroless nickel, electroless palladium, immersion gold(ENEPIG). In other embodiments, the pad protection layers 16 are each aself-assembled monolayer and can comprise Alkane with a number of carbonatoms between 4 and 30 and with a functional group like a thiol group oran alcohol group formed by immersion, spin coating, printing, the like,or a combination thereof.

In FIG. 4, stud bulbs 18 are formed on respective pad protection layers16. The stud bulbs 18 are formed, for example, by melting tips of wiresto form a sphere at each tip of the wires. The spheres are then placedon the pad protection layers 16, and a mechanical force, heat, and/orultrasonic energy is applied to bond the spheres to the pad protectionlayers 16. The wires are then broken above the spheres (or what waspreviously the spheres since the force, heat, and/or ultrasonic energymay have changed the shape). The wires used in this step can be copper,gold, aluminum, silver, an alloy, the like, or a combination thereof.The wires can also have doping elements in the metal. Further, the wirescan be a first metal coated with a second metal, for example, a copperwire coated with palladium. The wires can have a diameter betweenapproximately 0.3 mils and approximately 5 mils, such as approximately1.5 mils. The stud bulbs 18 can therefore comprise the same material asthe wires.

In FIG. 5, bulb protection coatings 20 are formed on respective studbulbs 18. The bulb protection coatings 20, in some embodiments, are ametal, a metal alloy, layers of a metal(s) or metal alloy(s), the like,or a combination thereof. Examples of metals include tin, nickel,palladium, gold, silver, the like, or a combination thereof. The bulbprotection coatings 20 may be formed, for example, by immersion plating,electro-plating, electroless-plating, the like, or a combinationthereof. In an embodiment, the bulb protection coatings 20 are tinformed by immersion plating. In another embodiment, the bulb protectioncoatings 20 are ENEPIG. In other embodiments, the bulb protectioncoatings 20 are each a self-assembled monolayer, such as Alkane with anumber of carbon atoms between 4 and 30 and with a functional group likea thiol group or an alcohol group formed by immersion, spin coating,printing, the like, or a combination thereof. In further embodiments,the bulb protection coatings 20 are each an OSP formed by acceptabletechniques. The bulb protection coatings 20 may provide a layer on thestud bulbs 18 to prevent the stud bulbs 18 from oxidizing, for example,from having a copper oxide formed on the stud bulbs 18 when the studbulbs are copper.

In FIG. 6, a second substrate 22, for example, a top substrate, isprovided. The second substrate 22 may have any of the features and/orcomponents previously discussed with respect to the first substrate 10.The second substrate 22 has pads 24 on a bottom surface of the secondsubstrate 22. The pads 24, in an embodiment, are formed directlyconnected to respective patterns in a metallization through apassivation layer. In another embodiment, the pads 24 are each a patternin a metallization layer. In further embodiments, the pads 24 can berespective exposed portions of through vias and/or can be formed onrespective portions of through vias. The pads 24, in an embodiment, area metal, a metal alloy, or layers of a metal(s) and/or metal alloy. Inthis embodiment, the pads 24 are copper, and in other embodiments, thepads 24 may comprise copper, gold, aluminum, aluminum copper (Al(Cu)),the like, or a combination thereof. The pads 24 provide an exteriorelectrical connection to various devices and/or components within and/orcoupled to the second substrate 22. A solder 26 is provided on the pads24. The solder 26 can be any solder material, such as lead free solderor the like, formed by acceptable methods.

In FIG. 7, the solder 26 on the second substrate 22 is brought intocontact with the stud bulbs 18 on the first substrate 10 and is reflowedto form reflowed solder connectors 28. The reflowed solder connectors 28provide mechanical and electrical connections between the stud bulbs 18on the first substrate 10 and the pads 24 on the second substrate 22. InFIG. 8, a molding compound 30 is dispensed in the space between thefirst substrate 10 and the second substrate 22 and around theconnections made between the substrates 10 and 22. The molding compound30 may be an acceptable material, such as an epoxy or the like. In otherembodiments, an underfill material, a non-conductive paste (NCP), anon-conductive film (NCF), or other dielectric film can be used in theplace of the molding compound 30.

It is worth noting that embodiments such as the structure shown in FIG.8 contemplate various additional features that are not explicitly shownin the figures. For example, the substrates 10 and 22 can each haveadditional electrical connectors on additional surfaces. The bottomsurface of first substrate 10 and the top surface of the secondsubstrate 22 can have stud bulbs, microbumps, minibumps, pillars,columns, BGA balls, controlled collapse chip connection (C4) bumps, thelike, or a combination thereof. Additionally, dies can be on varioussurfaces of the substrates 10 and 22. For example, a die(s) can beattached by electrical connectors to the bottom and/or to the topsurfaces of each of the substrates 10 and 22. Any number of dies can beon any surface. Further features of embodiments will be readily apparentto a person having ordinary skill in the art.

FIGS. 9 through 14 illustrate a second method of forming a PoP structureaccording to an embodiment. According to this embodiment, the firstsubstrate 10 and pads 12 are processed according to the steps discussedwith respect to FIGS. 1 and 2. In FIG. 9, the top surfaces of the pads12 are treated to form treated surfaces 32. The treatment can be aprocess to enhance the bonding of later formed stud bulbs with the pads12. In an embodiment, the treatment includes using an ammonia (NH₃),argon (Ar), oxygen (O₂), ozone (O₃), hydrogen (H₂), nitrogen (N₂), ormethane (CH₄) plasma. In another embodiment, the treatment includesdoping the pads 12 with germanium (Ge). Other plasma treatments ordopants can be used, as a person having ordinary skill in the art willreadily understand.

In FIG. 10, stud bulbs 18 are formed on the treated surfaces 32 in thesame or similar manner as previously discussed with regard to FIG. 4. InFIG. 11, bulb protection coatings 20 are formed on respective stud bulbs18 in the same or similar manner as previously discussed with regard toFIG. 5. FIGS. 12 through 14 illustrate providing the second substrate22, attaching the first substrate 10 to the second substrate 22 byreflowing, and providing a molding compound 30 between the substrates 10and 22 in the same or similar manner as previously discussed with regardto FIGS. 6 through 8. As with the previous embodiment, the structure ofFIG. 14 may have features that are not explicitly shown.

FIGS. 15 through 19 illustrate a third method of forming a PoP structureaccording to an embodiment. According to this embodiment, the firstsubstrate 10 and pads 12 are processed according to the steps discussedwith respect to FIGS. 1 and 2. In FIG. 15, stud bulbs 18 are formeddirectly on the pads 12 in the same or similar manner as previouslydiscussed with regard to FIG. 4. In this embodiment, the stud bulbs 18may be bonded by a direct metal-metal bond to the pads 12. The studbulbs 18 may be a same material as the pads 12, such as copper,aluminum, aluminum copper (Al(Cu)), the like, or a combination thereof.In another embodiment, the stud bulbs 18 may comprise a differentmaterial than the pads 12, for example, the stud bulbs 18 can comprisecopper while the pads 12 comprise aluminum or aluminum copper. FIGS. 16through 19 illustrate forming the bulb protection coatings 20 onrespective stud bulbs 18, providing the second substrate 22, attachingthe first substrate 10 to the second substrate 22 by reflowing, andproviding a molding compound 30 between the substrates 10 and 22 in thesame or similar manner as previously discussed with regard to FIGS. 5through 8. As with the previous embodiments, the structure of FIG. 19may have features that are not explicitly shown.

FIGS. 20 through 24 illustrate various features of stud bulbs accordingto embodiments. Any of these features can be incorporated or used in theforegoing embodiments. FIG. 20 illustrates a single stud bulb 40, suchas the stud bulb 18 illustrated in the foregoing figures. The singlestud bulb 40 is formed, for example, by melting a tip of a wire to forma sphere at the tip. The sphere is then placed on a bonding surface, anda mechanical force, heat, and/or ultrasonic energy is applied to bondthe sphere to the bonding surface. The wire is then broken above thesphere (or what was previously the sphere since the force, heat, and/orultrasonic energy may have changed the shape). The single stud bulb 40has a diameter D between approximately 0.3 mils and approximately 5mils, such as approximately 1.5 mils, and the single stud bulb 40 has aheight H between approximately 20 micrometers and approximately 200micrometers, such as approximately 150 micrometers.

FIG. 21 illustrates a single stud bulb 42 with an elongated tail 44. Thesingle stud bulb 42 with elongated tail 44 is formed, for example, in asimilar manner as the single stud bulb 40 in FIG. 20, except that thewire is broken at some distance from the single stud bulb 42 such thatthe elongated tail 44 remains. In other embodiments, other processparameters can be modified to form the elongated tail 44. The elongatedtail 44 has a height H1 between approximately 10 micrometers andapproximately 200 micrometers, such as approximately 100 micrometers,and the single stud bulb 42 has a height H2 between approximately 5micrometers and approximately 80 micrometers, such as approximately 50micrometers.

FIGS. 22 and 23 each show stacked single stud bulbs. In FIG. 22, thesingle stud bulbs 46 and 48 can be formed sequentially in the same orsimilar manner as the single stud bulb 40 in FIG. 20. The single studbulbs 46 and 48 in this embodiment are a same material. For example,each of the single stud bulbs 46 and 48 is copper. In FIG. 23, thesingle stud bulbs 50 and 52 can be formed sequentially in the same orsimilar manner as the single stud bulb 40 in FIG. 20. The single studbulbs 50 and 52 in this embodiment comprise different materials. Forexample, the single stud bulb 50 is gold, and the single stud bulb 52 iscopper. Although only two single stud bulbs are illustrated in FIGS. 22and 23, other embodiments contemplate more single stud bulbs that arestacked and/or comprising various combinations of materials.

FIG. 24 illustrates stacked single stud bulbs, one of which having anelongated tail. Single stud bulb 56 with elongated tail 58 is formedstacked on single stud bulb 54. The single stud bulb 54 is formed, forexample, in the same or similar manner as the single stud bulb of FIG.20, and the single stud bulb 56 with elongated tail 58 is formed, forexample, in the same or similar manner as the single stud bulb 42 withelongated tail 44 of FIG. 21. The stud bulbs 54 and 56 and elongatedtail 58 may include the same material(s) or different materials, such asdiscussed with respect to FIGS. 22 and 23, and further, may haveadditional single stud bulbs stacked.

FIGS. 25 through 28 illustrate various aspects of embodiments. FIGS. 25and 26 show an example pad 12, pad protection layer 16, stud bulb 18,bulb protection coating 20, reflowed solder connector 28, and pad 24,such as shown in FIG. 8. FIG. 25 shows a single stud bulb 18 a as thestud bulb 18, and FIG. 26 shows a single stud bulb 18 b with a greaterheight and/or an elongated tail as the stud bulb 18. In FIGS. 25 and 26,the pad protection layer 16 is an ENEPIG structure, for example. Thereflowed solder connector 28 is wetted to the top surface of the padprotection layer 16 such that the entirety of the top surface of the padprotection layer 16 outside of the stud bulb 18 is contacted by thereflowed solder connector 28. It should be noted that the entirety ofthe top surface is understood to include substantially the entirety ofthe top surface, such as would result in accordance with appropriateprocesses, like those disclosed herein, as a person having ordinaryskill in the art would understand the term.

Although not expressly illustrated, the reflowed solder connector 28 canbe wetted to the top surface of the treated surface 32 (FIG. 14) and/orthe pad 12 (FIG. 19) when those respective surfaces are used as thebonding surface of the stud bulb 18, similar to what is shown in FIGS.25 and 26. In other embodiments, the reflowed solder connector 28 maynot be wetted to the top surface of the treated surface 32 and/or thepad 12.

FIGS. 27 and 28 show an example pad 12, pad protection layer 16, studbulb 18, bulb protection coating 20, reflowed solder connector 28, andpad 24, such as shown in FIG. 8. FIG. 27 shows a single stud bulb 18 aas the stud bulb 18, and FIG. 28 shows a single stud bulb 18 b with agreater height and/or an elongated tail as the stud bulb 18. In FIGS. 27and 28, the pad protection layer 16 is an immersion tin, self-assembledmonolayer, or OSP structure, for example. The reflowed solder connector28 is not wetted to the top surface of the pad protection layer 16, andportions 70, such as along the periphery, of the pad protection layer 16are not contacted by the reflowed solder connector 28 and are exposed.

FIG. 29 illustrates a partial joint. A partial joint is formed, forexample, when an amount of solder 26 is not sufficient to formcompletely over the stud bulb 18 when reflowed. FIG. 29 shows a studbulb 18 b with a great height and/or elongated tail bonded to a bondingsurface 72. A bulb protection coating 20 is on the stud bulb 18 b.Reflowed solder connector 28 is reflowed around the stud bulb 18 b andconnected to bonding surface 74. The bonding surface 72 can be the padprotection layer 16, treated surface 32, or the pad 12, and the bondingsurface 74 can be the pad 24, for example. The reflowed solder connector28 does not completely cover the stud bulb 18 b, and a portion of thebulb protection coating 20 is exposed. It should be noted that variousconfigurations of the stud bulb can be used, such as a single stud bulb,stacked single stud bulbs, a single stud bulb with a great height, asingle stud bulb with an elongated tail, or a combination thereof.

FIGS. 30 through 33 illustrate various modifications to a stud bulbaccording to embodiments. FIG. 30 depicts the structure of FIG. 25, forexample, except including an inter-metal compound (IMC) 80. The IMC 80is formed on portions of the pad protection layer 16 that the reflowedsolder contacts during the reflow process. The IMC 80 can be formed byincluding a material in the solder 26 that reacts with the padprotection layer 16 during the reflow process. The IMC 80 can be acopper tin (for example, Cu₃Sn or Cu₆Sn₅), nickel tin (for example,Ni₃Sn₄), the like, or a combination thereof.

FIG. 31 depicts the structure of FIG. 27, for example, except includingan IMC 82 and without the bulb protection coating 20. The IMC 82 isformed on portions of the stud bulb 18 a that the reflowed soldercontacts during the reflow process. The IMC 82 can be formed byincluding a material in the solder 26 that reacts with the stud bulb 18a during the reflow process. The IMC 82 can be a copper tin (forexample, Cu₃Sn or Cu₆Sn₅) or the like.

In embodiments like that shown in FIG. 31, a bulb protection coating 20may or may not be formed on the stud bulb 18 a before reflowing thesolder 26. If no bulb protection coating 20 is formed, the IMC 82 formsdirectly on the stud bulb 18 a as discussed. If a bulb protectioncoating 20 is formed, in embodiments, the bulb protection coating 20 candissolve during the reflowing, and the IMC 82 forms directly on the studbulb 18 a. Further, although not expressly depicted, embodimentscontemplate a stud bulb 18 a that has a bulb protection coating 20 on anouter surface of the stud bulb 18 a, and the IMC 82 is formed on anouter surface of the bulb protection coating 20. In such a situation,the IMC 82 can be similarly formed as discussed with respect to FIG. 31.

FIG. 32 depicts the structure of FIG. 30, for example, except includingan IMC 82 and without the bulb protection coating 20. The IMC 82 isformed on portions of the stud bulb 18 a that the reflowed soldercontacts during the reflow process. The IMC 82 can be a copper tin (forexample, Cu₃Sn or Cu₆Sn₅) or the like.

In embodiments like that shown in FIG. 32, a bulb protection coating 20may or may not be formed on the stud bulb 18 a before reflowing thesolder 26. If no bulb protection coating 20 is formed, the IMC 82 formsdirectly on the stud bulb 18 a as discussed. If a bulb protectioncoating 20 is formed, in embodiments, the bulb protection coating 20 candissolve during the reflowing, and the IMC 82 forms directly on the studbulb 18 a. Further, although not expressly depicted, embodimentscontemplate a stud bulb 18 a that has a bulb protection coating 20 on anouter surface of the stud bulb 18 a, and the IMC 82 is formed on anouter surface of the bulb protection coating 20. In such a situation,the IMC 82 can be similarly formed as discussed with respect to FIG. 32.

FIG. 33 depicts the structure of FIG. 29, for example, except includingan IMC 84 and without the bulb protection coating 20. The IMC 84 isformed on portions of the stud bulb 18 b that the reflowed soldercontacts during the reflow process. As with the partial joint previouslydiscussed, a portion of the stud bulb 18 b is not covered by the IMC 84or the reflowed solder connector 28. The IMC 84 can be formed byincluding a material in the solder 26 that reacts with the stud bulb 18b during the reflow process. The IMC 84 can be a copper tin (forexample, Cu₃Sn or Cu₆Sn₅) or the like.

In embodiments like that shown in FIG. 33, a bulb protection coating 20may or may not be formed on the stud bulb 18 b before reflowing thesolder 26. If no bulb protection coating 20 is formed, the IMC 84 formsdirectly on the stud bulb 18 b as discussed. If a bulb protectioncoating 20 is formed, in embodiments, the bulb protection coating 20 candissolve during the reflowing, and the IMC 84 forms directly on the studbulb 18 b. Further, although not expressly depicted, embodimentscontemplate a stud bulb 18 b that has a bulb protection coating 20 on anouter surface of the stud bulb 18 b and the IMC 84 on an outer surfaceof the bulb protection coating 20. In such a situation, the IMC 84 canbe similarly formed as discussed with respect to FIG. 33.

FIGS. 34 and 35 depict a layout view and a cross section view,respectively, of components of a package structure. The structureincludes a substrate 90 such as the first substrate 10 in aboveembodiments, stud bulbs 92 on a top surface of the substrate 90, and adie 94 attached on the top surface of the substrate 90. As shown in FIG.35, electrical connectors 96 connect the die 94 to the substrate 90. Theelectrical connectors 96 can be, for example, microbumps, minibumps, C4bumps, or the like. FIGS. 34 and 35 also illustrate a pitch P betweenthe stud bulbs 92. The pitch is, for example, below 100 micrometers, orbetween approximately 50 micrometers and approximately 90 micrometers,such as approximately 80 micrometers. It should be noted that thestructure can be a bottom substrate in a PoP structure and can have, forexample, BGA balls on the bottom surface. Further, additional packagestructures can be over the top surface of the structure to form a PoPstructure, such as shown in the embodiments in FIGS. 1 through 19.

FIG. 36 illustrates an example PoP structure according to an embodiment.The structure in FIG. 36 includes components discussed with respect toFIGS. 34 and 35. The structure further includes electrical connectors98, such as BGA balls, on a bottom surface of the substrate 90.Additionally, a second substrate 102 is attached to the substrate 90 byreflowed solder connectors 100, which are coupled to a bottom surface ofthe second substrate. The reflowed solder connectors 100 are reflowedaround the stud bulbs 92 as discussed in previous embodiments. A seconddie 104 is attached to a top surface of the second substrate 102 byelectrical connectors 106, which can be the same as or similar to theelectrical connectors 96. Features of stud bulbs and other componentspreviously discussed can be incorporated into the structure in FIG. 36.Further, additional dies can be on the structure, such as on bottomsurfaces of the substrates 90 and 102 and/or on the top surfaces of thesubstrates 90 and 102. Even further, additional package structures canbe on the top surface of the second substrate 102 which may or may notuse stud bulbs or other features discussed herein.

FIGS. 37 through 40 illustrate various package structures incorporatingfeatures previously discussed, which also may be used in the PoPstructure of FIG. 36. FIGS. 37 through 40 include components of FIGS. 34and 35, and as such, explicit discussion of those components is omittedwith regard to FIGS. 37 through 40. In FIG. 37, the package includesstud bulbs 110 that have a height that extends above a top surface ofthe die 94. The stud bulbs 110 have a height, for example, betweenapproximately 20 micrometers and approximately 80 micrometers, such asapproximately 50 micrometers, and a diameter, for example, betweenapproximately 10 micrometers and approximately 80 micrometers, such asapproximately 30 micrometers.

In FIG. 38, the package structure includes stacked stud bulbs 112 thateach comprise two single stud bulbs. The stacked stud bulbs 112 have aheight that extends above a top surface of the die 94. The stacked studbulbs 112 have a height, for example, between approximately 30micrometers and approximately 200 micrometers, such as approximately 150micrometers, and a diameter, for example, between approximately 20micrometers and approximately 150 micrometers, such as approximately 80micrometers.

In FIG. 39, the package structure includes stud bulbs 114 with elongatedtails. The stud bulbs 114 with elongated tails have a height thatextends above a top surface of the die 94. The stud bulbs 114 withelongated tails have a height, for example, between approximately 30micrometers and approximately 200 micrometers, such as approximately 150micrometers, and a diameter, for example, between approximately 20micrometers and approximately 150 micrometers, such as approximately 80micrometers.

In FIG. 40, the package includes stud bulbs 116 that have a height thatextends to a point that is below a top surface of the die 94. The studbulbs 116 have a height, for example, between approximately 10micrometers and approximately 50 micrometers, such as approximately 30micrometers, and a diameter, for example, between approximately 5micrometers and approximately 50 micrometers, such as approximately 30micrometers. In an embodiment, in a process for forming the stud bulbs116 includes reducing the height and/or diameter of the stud bulbs by,for example, laser drilling.

By having stud bulbs in a PoP structure, a pitch between connectorsinterconnecting the packages can be decreased, for example, below 100micrometers, and thus, the density of the connectors can be increased.Further, in embodiments, the height and the pitch of the stud bulbs canbe controlled by the selection of wires and/or by process parametercontrol. A process for creating the stud bulbs can be flexible andapplied for various package sizes. Also, embodiments can use variousmaterials that are compatible with conventional processes.

A first embodiment is a structure. The structure comprises a firstsubstrate, stud bulbs, a die, a second substrate, and electricalconnectors. The stud bulbs are coupled to a first surface of the firstsubstrate. The die is attached to the first surface of the firstsubstrate. The electrical connectors are coupled to the secondsubstrate, and respective ones of the electrical connectors are coupledto respective ones of the stud bulbs.

Another embodiment is a structure. The structure comprises a firstsubstrate, a second substrate, a stud bulb, and a solder connector. Thefirst substrate comprises a first pad on a first surface of the firstsubstrate, and a die is attached to the first surface of the firstsubstrate. The second substrate comprises a second pad on a firstsurface of the second substrate. The stud bulb is on the first pad, andthe solder connector couples the stud bulb to the second pad.

A further embodiment is a method. The method comprises providing a firstsubstrate, a first pad being on a first surface of the first substrate,a die being attached to the first surface of the first substrate;forming a stud bulb on the first pad; providing a second substrate, asecond pad being on a first surface of the second substrate; andcoupling a solder connector to the stud bulb and to the second pad.

An even further embodiment is a structure. The structure comprises afirst bond pad on a first surface of a first substrate, a die attachedto the first surface of the first substrate, a second bond pad on asecond surface of a second substrate, a stud bulb on the first bond pad,and solder mechanically coupling the stud bulb to the second bond pad.The first surface opposes the second surface, and the die is disposedbetween the first surface and the second surface.

Although the present embodiments and their advantages have beendescribed in detail, it should be understood that various changes,substitutions and alterations can be made herein without departing fromthe spirit and scope of the disclosure as defined by the appendedclaims. Moreover, the scope of the present application is not intendedto be limited to the particular embodiments of the process, machine,manufacture, composition of matter, means, methods and steps describedin the specification. As one of ordinary skill in the art will readilyappreciate from the disclosure, processes, machines, manufacture,compositions of matter, means, methods, or steps, presently existing orlater to be developed, that perform substantially the same function orachieve substantially the same result as the corresponding embodimentsdescribed herein may be utilized according to the present disclosure.Accordingly, the appended claims are intended to include within theirscope such processes, machines, manufacture, compositions of matter,means, methods, or steps.

What is claimed is:
 1. A structure comprising: a first substrate; studbulbs coupled to a first surface of the first substrate, the stud bulbscomprising a first material composition; a die attached to the firstsurface of the first substrate; a second substrate; solder electricalconnectors coupled to the second substrate, the solder electricalconnectors comprising a second material composition, the second materialcomposition being different from the first material composition,respective ones of the solder electrical connectors coupling respectiveones of the stud bulbs; and respective ones of protection coatings on asurface of the respective ones of the stud bulbs, the respective ones ofthe protection coatings being between the respective ones of the studbulbs and the respective ones of the solder electrical connectors, theprotection coatings comprising a third material composition, the thirdmaterial composition being different from the first material compositionand the second material composition.
 2. The structure of claim 1,wherein the first substrate comprises pads, respective ones of padprotection layers being over respective ones of the pads, the respectiveones of the stud bulbs being bonded to the respective ones of the padprotection layers.
 3. The structure of claim 1, wherein the firstsubstrate comprises pads, respective ones of the pads comprisingrespective ones of treated surfaces, the respective ones of the studbulbs being bonded to respective ones of the treated surfaces.
 4. Thestructure of claim 1, wherein the first substrate comprises pads, therespective ones of the stud bulbs being bonded directly to respectiveones of the pads.
 5. The structure of claim 1, wherein each of the studbulbs comprises (i) a single stud bulb, (ii) a single stud bulb with anelongated tail, (iii) stacked at least two single stud bulbs, (iv) afirst single stud bulb with an elongated tail stacked on a second singlestud bulb, or (v) a combination thereof.
 6. The structure of claim 1,wherein the respective ones of the stud bulbs and the respective ones ofthe solder electrical connectors form a partial joint.
 7. A structurecomprising: a first substrate having a first pad on a first surface ofthe first substrate, a die being attached to the first surface of thefirst substrate; a second substrate having a second pad on a firstsurface of the second substrate; a stud bulb comprising a first materialcomposition and on the first pad; a protection coating comprising asecond material composition and on a surface of the stud bulb, thesecond material composition being different from the first materialcomposition; and a solder connector comprising a third materialcomposition and coupling the stud bulb to the second pad, the thirdmaterial composition being different from the first material compositionand the second material composition.
 8. The structure of claim 7,wherein the first pad comprises a pad protection layer or a treatedsurface adjacent the stud bulb.
 9. The structure of claim 7, wherein thestud bulb is directly bonded to the first pad by a metal-metal bond. 10.The structure of claim 7, wherein the stud bulb is a single stud bulbwith an elongated tail.
 11. The structure of claim 7, wherein the studbulb comprises a first stud bulb stacked on a second stud bulb.
 12. Thestructure of claim 11, wherein the first stud bulb is a single stud bulbwith an elongated tail, and the second stud bulb is a single stud bulb.13. The structure of claim 7, wherein the solder connector does notcompletely cover a surface of the stud bulb, the surface not beingbonded to the pad.
 14. A structure comprising: a first bond pad on afirst surface of a first substrate; a die attached to the first surfaceof the first substrate; a second bond pad on a second surface of asecond substrate, the first surface opposing the second surface, the diebeing disposed between the first surface and the second surface; a studbulb comprising a first material composition and on the first bond pad;a protection coating comprising a second material composition and on asurface of the stud bulb, the second material composition beingdifferent from the first material composition; and solder comprising athird material composition and mechanically coupling the protectioncoating to the second bond pad, the third material composition beingdifferent from the first material composition and the second materialcomposition.
 15. The structure of claim 14, wherein the first bond pad(i) comprises a pad protection layer adjacent the stud bulb, (ii)comprises a treated surface adjacent the stud bulb, or (iii) is directlybonded to the stud bulb by a metal-metal bond.
 16. The structure ofclaim 14, wherein the stud bulb comprises (i) a single stud bulb, (ii) asingle stud bulb with an elongated tail, (iii) stacked at least twosingle stud bulbs, (iv) a first single stud bulb with an elongated tailstacked on a second single stud bulb, or (v) a combination thereof.